Field
The present application relates to an acoustic sensor.
Background
Electret condenser microphones (ECMs) incorporating acoustic sensors are miniature microphones that have been used conventionally. However, ECMs are weak against heat, and are less suited to digitization and miniaturization than MEMS microphones, which incorporate acoustic sensors fabricated with micro electro mechanical systems (MEMS). Such MEMS microphones are increasingly used nowadays (refer to, for example, Patent Literatures 1 to 4).
One type of acoustic sensor using the MEMS technique includes a back plate to which an electrode film is fixed, and a vibrating electrode film, which vibrates in response to sound waves, arranged to face the back plate with a space formed between them. This acoustic sensor can be fabricated by, for example, forming a vibrating electrode film on a substrate, forming a sacrificial layer over the vibrating electrode film, and forming a back plate on the sacrificial layer, and then removing the sacrificial layer. The MEMS technique, which uses a semiconductor fabrication technique, can produce an extremely small acoustic sensor. However, such an acoustic sensor fabricated with the MEMS technique may typically include a thin vibrating electrode film to detect an extremely low pressure, and a back plate. Unlike other sensors that simply detect pressure, the acoustic sensor provides good acoustic characteristics by placing the vibrating electrode film suspended from the substrate to form a ventilation hole. This vibrating electrode film thus uses a soft support. In this case, the acoustic sensor tends to be less strong, and may not have high resistance to impact. Parts of the vibrating electrode film and the back plate that are structurally likely to receive stress may be reinforced, but such reinforced parts may cause more stress applied to other parts.